Electroluminescent panels (ELP's) are generally coupled to an associated controller board with flexible circuits (FC's) having drive circuitry that interconnects electrical signals between rows of contacts on the perimeter of the ELP and the controller board. Several categories of such couplings are used for this such purpose, such as those of the anisotropic adhesive, the direct pad-to-pad welded, the elastic interlayered, and the direct pressure contact types.
Anisotropic adhesives provide one sort of coupling between ELP's and FC's. These adhesives comprise an adhesive layer filled with electrically conductive microspheres brought into contact with each other and with respective mutually aligned contact pads on the ELP and FC's under localized pressure from these pads on the opposite sides of the layer.
Anisotropic adhesives have numerous disadvantages for use as such interconnects. These disadvantages include the need for dispensing equipment, limited adhesive shelf life, difficulty of disassembly and repair, and possibility of contact-point migration in the direction of thermoexpansion or thermocontraction that contributes to possible shorts with adjacent ELP contacts.
Direct pad-to-pad welding or bonding provides another sort of coupling between ELP's and FC's. Such connections are extremely difficult to disassemble and repair, and assembly requires the use of complex and expensive equipment. Due to a considerable thermoexpansion coefficient mismatch between known ELP and FC materials, the cyclical increases in the interconnect temperature from its assembly to full power-up result in rather high shear stress in the bonds and respective flexural loads on the glass, potentially leading to failures.
An elastomeric interlayer compressed between the ELP and FC's provides still another sort of coupling between the ELP and FC's. Unidirectional conductivity through the elastomeric interlayer between the contacts on the ELP and the FC's is provided by the compressed regions of the interlayer along metal traces on the surface of the interlayer or metal particles through the interlayer.
Such couplings require high rigidity for maintaining the degree of compression necessary to maintain sufficient electrical contact. The extra parts and space required to establish and maintain this compression increase the complication and size of the coupling. There is also a possibility of contact-point migration in the direction of thermoexpansion or thermocontraction, causing shorts between adjacent contacts of the ELP and FC's.
A significant improvement over the above described types of connectors is the direct pressure contract connector. Various types of direct pressure contact connectors are known that are useable for coupling the ELP to the FC's. Such connectors are more desirable than the other types described above, especially the adhesive types, because they are generally removable and they can be designed to require no insertion force for installation. One example of such a connector comprises clip members that are used to fasten planar electrical terminations on a panel to planar electrical terminations on flexible interconnection strips.
A special mounting tool is used to mount and remove each clip along the edge of the panel with zero insertion force. The mounting and removal of the clips with the special tool requires a large amount of clearance around the edges of the panel.
Another example of a direct pressure contact connector that provides zero insertion force between electrical terminations on a panel and on flexible interconnection strips has a clamping bar that clamps the flexible strips against the panel with a plurality of springs as the connector is engaged with the edge of the panel. This connector requires a large amount of clearance around the edge of the ELP for installation. The springs concentrate the applied force along a narrow lengthwise strip of the ELP-FC interface, so that a large amount of spring force may provide still less than optimal electrical contact.